With the progress and development of industrialization, vacuum furnace plays an irreplaceable role in mould production. It is mainly used in ceramic firing, vacuum smelting, degassing of electric vacuum parts, annealing, brazing of metal parts, and ceramic-metal sealing. Vacuum heat treatment of vacuum furnace can realize almost all heat treatment processes, such as quenching, annealing, tempering, carburizing, nitriding, gas quenching, oil quenching, nitrate quenching, water quenching, vacuum brazing, sintering, surface treatment and so on. Vacuum furnace has high thermal efficiency, can achieve rapid heating and cooling, can achieve no oxidation, no decarbonization, no carburization, can remove the phosphorus chip on the surface of the workpiece, and degreasing and degassing, so as to achieve the effect of surface bright purification.
Generally speaking, the processed workpiece is heated slowly in the furnace, the difference of internal heat temperature is small, and the thermal stress is small, so the deformation is small. The qualified rate of products is high. The utility model can reduce the cost and has the function of degassing, thereby improving the mechanical performance and service life of the work. Good working environment, safe operation, no pollution and pollution. The treated workpiece has no danger of hydrogen embrittlement. It can prevent surface hydrogen embrittlement of titanium and refractory metal shell. The vacuum heat treatment process has good stability and repeatability. With these advantages, the development of vacuum heat treatment equipment and technology has been paid more and more attention and applied more and more widely.
Vacuum heat treatment is a comprehensive technology combining vacuum technology with heat treatment. It refers to all and part of heat treatment process carried out in vacuum. China divides vacuum into low, medium, high and ultra-high vacuum.
Vacuum furnaces and medium frequency electric furnaces have good prospects in the field of thermal processing. They are used for induction heating of diathermy, rolling, forging, pipe bending, heat treatment (quenching), welding and other processes. So what are the heat treatment techniques of vacuum furnace and medium frequency furnace?
1. Nitrogen should not be used as cooling gas when titanium alloy is treated in vacuum furnace, because titanium and nitrogen react at high temperature to form golden titanium nitride.
2. All the movable connections of the vacuum furnace are sealed with O-type rubber rings, which are cooled by water.
3. Vacuum quenching oil should be used to quench the workpiece in vacuum, which has lower saturated vapor pressure.
4. Vacuum furnace maintenance should be in the state of vacuum or pure nitrogen, to avoid suction and moisture absorption when not in use at ordinary times.
5. The pressure rise rate of domestic vacuum furnaces should not be less than 1.33Pa/h, and the standard of some foreign enterprises should be 0.67Pa/h.
6. Vacuum heating is mainly radiation, and the workpiece should be kept spacing in the furnace.
7. During the heating process, the workpiece and the material in the furnace will deflate and the vacuum will decrease.
8. The heating temperatures of vacuum tempering, vacuum annealing, vacuum solid solution treatment and vacuum aging are generally the same as those of conventional treatment.
9. Vacuum tempering furnace should have quick cooling device. The pressure of cooling water should be greater than 0.2 Mpa and the flow rate should be adjustable.
10. Cooling gas: steel generally uses 99.995% pure nitrogen, superalloy 99.999% nitrogen or argon, titanium alloy 99.995% argon.
11. Warming up: After putting into the workpiece, it can be heated only when pre-pumped to 6.67 Pa.
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